The present invention relates to a filter for protecting electronic circuitry from electromagnetic field interference (EMI), over voltages and preventing electromagnetic emissions. More specifically, this invention relates to a multi-functional electronic component whose physical architecture suppresses unwanted electromagnetic emissions, both those received from other sources and those created internally within electronic circuitry by differential and common mode currents. In addition, due to the electronic component""s physical architecture and material composition, over voltage surge protection and magnetic properties can be integrally incorporated with the differential and common mode filtering.
The majority of electronic equipment produced presently, and in particular computers, communication systems, automobiles, military surveillance equipment, stereo and home entertainment equipment, televisions and other appliances include miniaturized components to perform new high speed functions and electrical interconnections which according to the materials from which they are made or their mere size are very susceptible to stray electrical energy created by electromagnetic interference or voltage transients occurring on electrical lines. Voltage transients can severely damage or destroy such micro-electronic components or contacts thereby rendering the electronic equipment inoperative, and requiring extensive repair and/or replacement at great cost.
Electrical interference in the form of EMI or RFI can be induced into electrical lines from such sources as radio broadcast antennas or other electromagnetic wave generators. EMI can also be generated from the electrical circuit which is desired to be shielded from EMI. Differential and common mode currents are typically generated in cables and on circuit board tracks. In many cases fields radiate from these conductors which act as antennas. Controlling these conducted/radiated emissions is necessary to prevent interference with other circuitry or other parts of the circuit generating or sensitive to the unwanted noise. Other sources of interference are generated from equipment coupled to the electrical lines, such as computers, switching power supplies and a variety of other systems, which may generate significant interference which is desired to be eliminated to meet international emission and/or susceptibility requirements.
Transient voltages occurring on electrical lines can be induced by lightning which produces extremely large potentials in a very short time. In a similar manner, nuclear electromagnetic pulses (EMP) generate even larger voltage spikes with faster rise time pulses over a broad frequency range which are detrimental to most electronic devices. Other sources of large voltage transients are found to be associated with voltage surges occurring upon the switching off or on of some electronic power equipment as well as ground loop interference caused by varying ground potentials. Existing protection devices, primarily due to their architecture and basic materials, do not provide adequate protection in a single integrated package.
Based upon the known phenomenon of electromagnetic emissions and transient voltage surges a variety of filter and surge suppression circuit configurations have been designed as is evident from the prior art. A detailed description of the various inventions in the prior art is disclosed in U.S. Pat. No. 5,142,430, herein incorporated by reference.
The ""430 patent itself is directed to power line filter and surge protection circuit components and the circuits in which they are used to form a protective device for electrical equipment. The circuit components comprise wafers or disks of material having desired electrical properties such as varistor or capacitor characteristics. The disks are provided with electrode patterns and insulating bands on surfaces thereof which coact with apertures formed therein so as to electrically connect the components to electrical conductors of a system easily and effectively. These electrode patterns act in conjunction with one another to form common electrodes with the material interposed there between. The ""430 patent was primarily directed toward filtering paired lines. The present invention improves on the paired line concept by refining and adapting the concept for use with low voltage low current data communication lines as well as arrangements directed towards high voltage industrial and home applications such as three phase power lines, electric motor noise filtering, LANs and other computer and electronic devices.
Therefore, in light of the foregoing deficiencies in the prior art, the applicant""s invention is herein presented.
Based upon the foregoing, there has been found a need to provide a multi-functioning electronic component which attenuates electromagnetic emissions resulting from differential and common mode currents flowing within electronic circuits, single lines, pairs of lines and multiple twisted pairs. Because of the sensitive nature of electronic technology there is also a need for combining electromagnetic filtering with surge protection to eliminate the susceptibility to over voltages and emissions from external sources. Due to the highly competitive nature of today""s electronic industry such a differential and common mode filter/surge protector must be inexpensive, miniaturized, low in cost and highly integrated to be incorporated into a plurality of electronic products.
It is therefore a main object of the invention to provide an easily manufactured and adaptable multi-functional electronic component which filters electromagnetic emissions caused by differential and common mode currents.
It is another object of the invention to provide a protective circuit arrangement which may be mass produced and adaptable to include one or more protective circuits in one component package to provide protection against voltage transients, over voltages and electromagnetic interference.
Another object of the invention is to provide protective circuits having an inherent ground which provides a path for attenuating EMI and over voltages without having to couple the hybrid electronic component to circuit or earth ground.
These and other objects and advantages of the invention are accomplished through the use of a plurality of common ground conductive plates surrounding corresponding electrode plates separated by a material which exhibits any one or a combination of a number of predetermined electrical properties. By coupling pairs of conductors to the plurality of common ground conductive plates and selectively coupling the conductors to electrode plates, line-to-line and line-to-ground component coupling is accomplished providing differential and common mode electromagnetic interference filtering and/or surge protection. The circuit arrangement comprises at least one line conditioning circuit component constructed as a plate. Electrode patterns are provided on one surface of the plate and the electrode surfaces are then electrically coupled to electrical conductors of the circuit. The electrode patterns, dielectric material employed and common ground conductive plates produce commonality between electrodes for the electrical conductors which produces a balanced (equal but opposite) circuit arrangement with an electrical component coupled line-to-line between the electrical conductors and line-to-ground from the individual electrical conductors.
The particular electrical effects of the differential and common mode filter are determined by the choice of material between the electrode plates and the use of ground shields which effectively house the electrode plates within one or more Faraday cages. If one specific dielectric material is chosen the resulting filter will be primarily a capacitive arrangement. The dielectric material in conjunction with the electrode plates and common ground conductive plates will combine to create a line-to-line capacitor and a line-to-ground capacitor from each individual electrical conductor. If a metal oxide varistor (MOV) material is used then the filter will be a capacitive filter with over current and surge protection characteristics provided by the MOV-type material. The common ground conductive plates and electrode plates will once again form line-to-line and line-to-ground capacitive plates providing differential and common mode filtering accept in the case of high transient voltage conditions. During these conditions the MOV-type varistor material, which is essentially a non-linear resistor used to suppress high voltage transients, will take effect to limit the voltage which may appear between the electrical conductors.
In a further embodiment a ferrite material may be used adding additional inherent inductance to the differential and common mode filter arrangement. As before, the common ground conductive and electrode plates form line-to-line and line-to-ground capacitive plates with the ferrite material adding inductance to the arrangement. Use of the ferrite material also provides transient voltage protection in that it to will become conductive at a certain voltage threshold allowing the excess transient voltage to be shunted to the common ground conductive plates, effectively limiting the voltage across the electrical conductors.
Numerous other arrangements and configurations are also disclosed which implement and build on the above objects and advantages of the invention to demonstrate the versatility and wide spread application of differential and common mode filters within the scope of the present invention.